The semiconductor industry and various other industries characterized by giant factories are facing an increasingly serious problem of ballooning equipment investments and operating costs due to their factory size, which are often greater than the production output and thereby make the business unprofitable.
A majority of the aforementioned manufacturing factories have manufacturing processes using clean rooms, except for chemical plants where clean rooms are not the best option for cleaning because their plants are even larger than those in other industries. Accordingly, the idea of reducing equipment investment by downgrading the clean rooms through various methods such as locally clean production methods is beginning to be recognized as an immediately effective solution to the aforementioned problem. In some industries these methods are already put into practical use and their use is spreading. Local cleanness also has the effect of reducing the environmental control cost of the factory.
The only example of applying a locally clean production method to all the processes of a factory is one described in Non-patent Literature 1 involving pre-processes for manufacturing semiconductor integrated circuits. The manufacturing system described therein transfers the wafer being manufactured, between independent manufacturing apparatuses in a box. Each of these apparatuses has a port. The port has two doors. One door connects the apparatus and the port, while the other door connects the port and the outside world. By operating the apparatus in such a way that one of the doors is always closed, the interior of the apparatus can always be isolated from the outside world. The wafer box is coupled to the port. When the wafer box is coupled to the port, the wafer ambience can be isolated from the outside world to some extent, thereby allowing the wafers to be exchanged between the box and the manufacturing apparatus.
The box must be light, small, and simple in its mechanism in order to make sure it can be easily transferred. To achieve this requirement, ingenious ideas are needed as to how the box should be opened and closed and especially how the box door should be stored when opened. To be specific, the mode of storing the box door in the wafer box when the port is coupled is against the aforementioned requirement because extra space is needed to store the door. Accordingly, an appropriate coupling structure is such that the wafer box door is stored inside the port. HP has obtained a patent (Patent Literature 1) pertaining to a coupling method that considers this point.
This patent is mainly characterized in that it has three subsystems including (1) a port, (2) a wafer transfer box, and (3) a wafer transfer mechanism inside the port, and that “the two doors are linked and moved into the clean interior space.” The name of this system, “Standard Mechanical InterFace, or SMIF” has subsequently become the standard name for this system. The reason why the two doors are linked is as follows. Fine particles are attached to the exterior surfaces of the two doors that are contacting the outside world containing fine particles. By linking the doors, these fine particles can be trapped between the doors and as the doors are stored inside the port, spreading of fine particles into the locally clean environment can be prevented.
As shown in FIG. 1(a), a box 1 comprises a box body 3 and a box door 4, while a port 2 comprises a port body 5 and a port door 6, and seals are provided in three locations including (a) between the box body 3 and box door 4, (b) between the port body 5 and port door 6, and (c) between the box body 3 and port body 5, where the three subsystems are needed as an axiom to perform transfer operations through separation of the interior and exterior, and therefore one key point of patentability of the SMIF patent lies in the sandwiching and trapping of fine particles attached to the surfaces of these two doors. However, sandwiched fine particles are not eliminated from this area. Also, no countermeasure is taken to control the risk of wafer contamination caused by fine particles dropping from the end faces of doors sandwiching them. In addition, structurally the port and wafer transfer box are not coupled in a hermetical manner, meaning that the structure presented by this patent does not function to completely prevent intrusion of external wafer contaminants into the port and wafer transfer box.
Asyst subsequently commercialized this SMIF system as a 200-mm wafer system. In relation to this practical system, Asyst patented an improvement mechanism for adding hermetical sealing to the SMIF system (Patent Literature 2). According to this patent, the coupling part comprises four structures, or namely a box, a box door, a port, and a port door. Also, this patent is characterized in that, as shown in FIG. 1(b), hermetical seals are provided between the contacting pairs of these four structures such as (a) between the box body 3 and box door 4, (b) between the port body 5 and port door 6, (c) between the box body 3 and port body 5, and (d) between the box door 4 and port door 6.
Thereafter, several patents of improvements to the aforementioned patent were registered in light of incompleteness of this sealing method. The specific patents cover a mechanism to replace or purge gas in the box (Patent Literature 3), a method to suppress generation of fine particles from the mechanical structure for latching the door (Patent Literature 4), and a method to suppress fine particles generated from the complex mechanical structure provided inside the box door, by using the effect of non-contact seal obtained by generating, in each movement stage for opening/closing the box door and apparatus door, a gas flow that causes fine particles to flow out of the apparatus and box (Patent Literature 5). However, this series of improvement patents created negative effects, as explained below, that made the mechanism more complex. The specific negative effects are increased manufacturing cost, increased weight, generation of new fine particle generation sources, and difficulty cleaning the box, among others. These improvement patents not only failed to isolate gas to a practically acceptable level, but they also failed to achieve complete isolation of fine particles. In addition, the fact that further improvements were necessary to suppress and eliminate generation of fine particles through the improvement patents, means that the SMIF system and the first four sealing methods implemented by Asyst cannot completely isolate fine particles and that they are not the best hermetical coupling system.
Thereafter in 2000 or thereabout, when the size of the latest wafers reached 300 mm, another SMIF system adopting sealing methods different from those of Asyst was proposed and became the global standard for 300-mm wafer transfer systems. This standard system is normally called the “Front-opening Interface Mechanical Standard, or FIMS.” This system, despite being a part of global SEMI standards (primarily SEMI Std. E57, E47.1, E62 and E63), is patented (Patent Literature 6). The FIMS adopts horizontal coupling to an opening provided in the horizontal direction from the box door.
This is in contrast to the vertical coupling method adopted by Asyst's system. Also, Asyst's vertical coupling system stores wafers in a cassette inside the box. Once coupled, the two linked doors are stored inside and then the entire cassette moves into the port. On the other hand, the FIMS has no cassette and the two doors linked in the horizontal direction move into the port and then drop vertically, after which the wafers in the box are directly taken out into the port using the wafer transfer robot provided in the port.
Furthermore, the FIMS patent is different from Asyst's patent in that it does not specifically define the sealing structure in the contact areas between structures. In an actual FIMS system put to practical use, a clearance of around 1 to 2 mm is intentionally provided between the structures. To be specific, such clearance is provided between the box and the port, and between the port and the port door. One reason for doing this is that any sealing structure based on physical contact generates mechanical rubbing in the seal area, which then causes a large amount of fine particles to generate. By providing no seals, the patent also differs from what is claimed in Asyst's patent. However, these clearances present a drawback in that theoretically, gas molecules cannot be sealed.
Asyst's 200-mm wafer system also has a pressure relief hole in the box that connects to the outside world for two purposes, one of which is to lessen the problem of fine particle generation caused by pressure change and consequent gas flow generating in the local environment as the box door and port door are opened and closed after coupling, and the other of which is to prevent the box door from becoming too tight due to negative pressure that might generate if the box is hermetical. This, in reality, structurally prevents isolation of, in particular, gas molecules. A pressure relief hole is also provided for the same reason in the box of the 300-mm wafer FIMS system, or Front Opening Unified Pod (FOUP). As described, conventional SMIF systems are not fully hermetical.
What is understood from the aforementioned conventional patents and known practical examples is that, while a locally clean production system with interior/exterior separation capability also effective on gas and other small molecules can be built with a hermetical mechanism having seals in respective areas, such system can produce a side effect of generating a large amount of fine particles due to mechanical rubbing, etc., of these seals. If a structure with clearances is used, on the other hand, generation of fine particles can be suppressed, but the interior and exterior cannot be separated in terms of gas molecules. This is a defect caused by a self-contradiction of the SMIF system. As a result, practical systems had no choice but to adopt an incompletely hermetical structure.
In fact, FIMS systems meeting the global standard that have been introduced to all semiconductor integrated circuit manufacturing factories supporting the latest 300-mm wafers have clearances and therefore cannot completely isolate not only gas molecules but also fine particles. One negative consequence of this is that, although a locally clean production system with complete isolation capability should eliminate the need for clean rooms, in reality all factories still operate their SMIF systems inside clean rooms. In other words, redundant cleanness is needed at the present, including clean rooms and local cleanness. This adds to equipment investment and requires high levels of management, which in turn pushes up the manufacturing cost to a significant extent.
Lastly, another important aspect, in addition to the aforementioned difficulty eliminating gas molecules and fine particles at the same time, is a need for a space called “port” to separate the apparatus space and human space. This necessitates a total of three doors, including two port doors and one transfer box door, which is essentially a cause of complexity of the coupling system.
Also, Patent Literatures 7 to 9 describe apparatuses, each of which has a pod contacting an apparatus in a manner allowing the pod door and apparatus port door to face each other, where these pod door and port door are moved to open the pod. However, the space formed by the pod door and apparatus port door is simply replaced by nitrogen and the surfaces of members defining the space are not cleaned, and if the interior of the pod or apparatus is vacuum, nitrogen replacement does not work due to pressure difference.
Patent Literature 10 describes a magnetic means and means using vacuum force for retaining the cap on the storage box, but these means only retain the cap and do not clean the cap surface or the surface of the apparatus door facing the cap.
The invention described in Patent Literature 11 joins the shutter-cum-lid of the vacuum clean box and the shutter of the clean apparatus in an airtight manner, after which the hermetical space is evacuated and then the shutter lid and shutter are opened separately. However, such method must be entirely implemented in vacuum and the exterior surfaces of all members must be cleaned beforehand.
The invention described in Patent Literature 12 evacuates the space formed by the lid of the exposure mask box and the lid of the apparatus and then opens these lids. However, this method can be used only for vacuum apparatuses and it simply creates vacuum and does not perform cleaning.